1. Field of the Invention
The present invention relates to a wireless asynchronous transfer mode: WATM) and, specifically, to an apparatus and method for adaptive hybrid automatic repeat request (ARQ) using a concatenated forward error correction (FEC), which controls the code rate of Reed Solomon (RS) code and complementary punctured convolutional (CPC) code according to channel environments to restore information with only transmitted sequence.
2. Discussion of Related Art
WATM systems are being studied for future broadband multimedia transmission. To support multimedia applications, WATM should provides quality of service (QOS) required by the type of transmitted data (data, voice, video). Accordingly, the WATM payload is coded so that various errors according to the QOS can be corrected.
There are two methods of correcting errors transmitted from a transmission side to a reception side. The first one is the forward error correction (FEC) which exchanges data in a continuous form between the transmission and reception sides without accepting interrupt. The second one is the automatic repeat request (ARQ) method in which, when an error is generated in a transmission section, the transmission side is informed of the generation of error and then repeatedly transmits the block having the error. This method makes periodic interrupt possible.
The FEC does not requires a buffer because data flow is not interrupted from the data generation source. Thus, this is used when the buffer is not able to be externally provided or there is no economy. Furthermore, the FEC is suitable for the public broadcasting channel which has various requests for the error rate and accepts a variety of users. Moreover, it is able to satisfy quality of service required by data even when a channel environment is not good. However, FEC coding needs unnecessary overheader to increase cost of apparatus, and deteriorates transmission efficiency in a good channel environment due to propagation delay.
The ARQ method is divided into a stop and wait ARQ, continuous ARQ, and adaptive ARQ. The ARQ need a reverse channel. The transmission side is required to be able to accept interrupt whenever a received data block has an error. Thus, when the reception side informs the transmission side of generation of error, the transmission side repeatedly transmits the data block having the error instead of a new data block. Accordingly, an ARQ system requires a buffer which stores the data block being transmitted. The size of the buffer is determined by the size and number of the data block stored therein. In the ARQ method, when an error creates in a block, retransmission is carried out without regard to the number of error bits which exist in the block. Accordingly, data is re-transmitted in blocks even if one error is generated in one block. This results in inefficient transmission. To improve the transmission efficiency and bandwidth efficiency, an FEC which is powerful and has variable code rate, ARQ and interleaving are required.
There has been proposed recently a hybrid ARQ method using a rate-compatible punctured convolutional (RCPC) code or rate-compatible convolutional (RCC) code for effectively increasing the transmission efficiency on the wireless ARM, to be adaptively used according to the channel environment. The hybrid ARQ method repeats transmission of spare bits which were not transmitted by a transmitter to a receiver according to perforation matrix when a transmitted data packet is lost or severely damaged. Then, the re-transmitted spare bits are combined with packets previously transmitted in order to form a convolutional code, to thereby restore the damaged packet.
As described above, the RCPC or RCC encoder provides the error correction capability which is varied with limited puncturing modes. In the hybrid ARQ method using the RCPC or RCC encoder, when data transmission is carried out from a transmitter to a receiver, the transmitter reduces the number of data bits being transmitted using perforation matrix to decrease overheader which creates during the transmission. Furthermore, when an error is generated in the transmitted data, the remaining data bits which were not transmitted by the perforation matrix is transmitted to be combined with the data previously transmitted, performing error correction.
The hybrid ARQ method, as described above, reduces the overheader which is generated when the data is transmitted from the transmitter to the receiver, and combines the transmitted data with the re-transmitted spare bit when the error creates in the transmitted data to restore the data information. The conventional ARQ method using the RCPC or RCC encoder is available in case that data is transmitted in a good environment so that the data is barely damaged. However, when the data is lost or severely damaged due to fading or interference in a poor environment, there is a limitation in restoring the data even if the spare bits are transmitted.
Accordingly, the present invention is directed to an apparatus and method for adaptive hybrid ARQ using a concatenated FEC that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus and method for adaptive hybrid ARQ using a concatenated FEC, which improves error correction capability of RS and CPC codes using a combining method to restore damaged data information with the help of data bits which are transmitted for error correction.
To accomplish the object of the present invention, there is provided an adaptive hybrid ARQ method using a concatenated FEC, which includes the steps of: puncturing a data packet to be transmitted to divide it into a first and second combined packets, encoding them with first perforation patterns different from each other, to generate a first and second transmission packets; selecting one of the first and second transmission packets and transmitting it to a receiver; the receiver generating a third combined packet using a perforation pattern corresponding the first transmission packet when it receives the first transmission packet; generating a first header packet and a first payload packet from the third combined packet and performing a first error detection; when any error is detected in the first error detection step, a transmitter sending the second transmission packet to the receiver, and the receiver generating a fourth combined packet using a perforation pattern corresponding to the second transmission packet; generating a second header packet and a second payload packet from the fourth combined packet and performing a second error detection; when any error is detected in the second error detection step, combining the first header packet with the second header packet, combining the first payload packet with the second payload packet, and performing a third error detection in the each combined packet; and when any error is not detected in the first, second and third error detection steps, completing data transmission.
Perforation pattern is transmitted, it is decoded using the second perforation pattern to generate a combined packet, and the combined packet is checked.
To accomplish the object of the present invention, there is also provided an adaptive hybrid ARQ apparatus using a concatenated FEC, the apparatus having a transmitter and a receiver, the transmitter including: an RS encoder for dividing transmission data into a header and payload and encoding each of them into an RS code; an interleaver for generating header packets and payload packets corresponding to code rates by puncturing a signal encoded by the RS encoder, combining each header packet with each payload packet, and interleaving the combined packets; and a CPC encoder for combining the interleaved packets with different perforation patterns.
To accomplish the object of the present invention, there is provided an adaptive hybrid ARQ apparatus using a concatenated FEC, the apparatus having a transmitter and a receiver, the receiver including: a buffer for storing transmission packets received from the transmitter; a CPC decoder for decoding the transmission packets stored in the buffer using different perforation patterns; a deinterleaver for deinterleaving a signal generated by the CPC decoder, to generate header packets and payload packets; and an RS decoder for decoding the header packets and payload packets generated by the deinterleaver into RS codes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.